This study is designed to identify the mechanisms involved in falling in the aged under both normal conditions and when postural stability and gait are degraded by alcohol. Year 1 will be spent gaining experience and collecting baseline data on the biomechanical and visual effects of acute alcohol consumption in 15 young males. Years 2 and 3 will then focus on a group of 40 elderly subjects (aged 65 to 75) to investigate the effects of alcohol on gait and posture under both normal and altered visual conditions. Detailed medical histories will be collected through administration of the DIS schedule and through thorough physical examinations, including measures of sensation and proprioception. The subjects' gait and posture will first be characterized under alcohol free conditions using quantitative biomechanical techniques. After the tasks have been performed under normal conditions, a variety of perturbations will be used to define the role of the various control and feedback systems in various tasks. The subjects will then be asked to perform the same postural and locomotor tasks after having consumed ethanol to raise their blood alcohol levels to 0.75 mg/ml(1.00mg/ml for young male subjects). Conduct of and recovery from all alcohol experiments will be closely supervised according to accepted practices in alcohol research. It is anticipated that this series of experiments will provide new information on a number of levels. First, we will develop highly specialized protocols for alcohol administration and testing on both young and elderly subjects. Second, new information is expected to be gained on the mechanisms controlling gait and posture in the elderly. Third, the effects of alcohol on gait and posture in the elderly will be defined. Fourth, the data are expected to provide a better basis for the understanding of falls in a variety of degradation conditions and to shed light on how they may be prevented.